U.S. patent application number 15/842891 was filed with the patent office on 2018-09-20 for proximity sensor and detecting method.
This patent application is currently assigned to OMRON Corporation. The applicant listed for this patent is OMRON Corporation. Invention is credited to Masayuki KOIZUMI, Yusuke NAKAYAMA, Minami WAZUMI.
Application Number | 20180267192 15/842891 |
Document ID | / |
Family ID | 63372482 |
Filed Date | 2018-09-20 |
United States Patent
Application |
20180267192 |
Kind Code |
A1 |
WAZUMI; Minami ; et
al. |
September 20, 2018 |
PROXIMITY SENSOR AND DETECTING METHOD
Abstract
A proximity sensor includes a transmission circuit that
periodically supplies an excitation current in a pulse form to a
detection coil for generating a magnetic field, a reception circuit
that detects voltages or currents generated at both ends of the
detection coil by the periodic supply of the excitation current,
and a controller that detects presence or a position of the
detection body by utilizing a time series signal obtained by the
detection. The controller acquires a factor that influences the
detection of the detection body in a first period of the time
series signal. The controller compensates a signal in a second
period of the time series signal by the factor. The controller
detects the presence or the position of the detection body on the
basis of a signal after the compensation.
Inventors: |
WAZUMI; Minami; (Nara-shi,
JP) ; KOIZUMI; Masayuki; (Nara-shi, JP) ;
NAKAYAMA; Yusuke; (Fukuchiyama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OMRON Corporation |
Kyoto |
|
JP |
|
|
Assignee: |
OMRON Corporation
KYOTO
JP
|
Family ID: |
63372482 |
Appl. No.: |
15/842891 |
Filed: |
December 15, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01V 3/38 20130101; G01V
3/10 20130101 |
International
Class: |
G01V 3/10 20060101
G01V003/10; G01V 3/38 20060101 G01V003/38 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2017 |
JP |
2017-049731 |
Claims
1. A proximity sensor that detects presence or position of a
detection body by utilizing a magnetic field, the proximity sensor
comprising: a detection coil that generates the magnetic field; a
transmission circuit that periodically supplies an excitation
current in a pulse form to the detection coil; a reception circuit
that performs detection of voltages or currents generated at both
ends of the detection coil by periodic supplying the excitation
current; and a controller that detects the presence or the position
of the detection body by utilizing a time series signal obtained by
the detection of the voltages or the currents generated at both
ends of the detection coil, wherein the controller acquires a first
factor that influences detection of the detection body in a first
period of the time series signal, performs compensation on a signal
in a second period of the time series signal by the first factor;
and detects the presence or the position of the detection body on
the basis of a signal after the compensation.
2. The proximity sensor according to claim 1, wherein the
controller acquires a second factor that influences the detection
of the detection body in a third period of the time series signal,
and compensates the signal in the second period of the time series
signal by the first factor and the second factor.
3. The proximity sensor according to claim 2, wherein the first
period and the third period are included in a period during which
the excitation current is supplied, and the second period is
included in a period during which supply of the excitation current
is blocked.
4. The proximity sensor according to claim 2, wherein the first
period, the second period, and the third period are included in a
period during which the excitation current is supplied.
5. The proximity sensor according to claim 2, wherein the first
period, the second period, and the third period are included in a
period during which supply of the excitation current is
blocked.
6. The proximity sensor according to claim 2, wherein any one of
the first factor and the second factor is a signal resulting from a
change in inductance of the detection coil, and the other is a
signal resulting from a change in resistance of the detection
coil.
7. The proximity sensor according to claim 3, wherein any one of
the first factor and the second factor is a signal resulting from a
change in inductance of the detection coil, and the other is a
signal resulting from a change in resistance of the detection
coil.
8. The proximity sensor according to claim 4, wherein any one of
the first factor and the second factor is a signal resulting from a
change in inductance of the detection coil, and the other is a
signal resulting from a change in resistance of the detection
coil.
9. The proximity sensor according to claim 5, wherein any one of
the first factor and the second factor is a signal resulting from a
change in inductance of the detection coil, and the other is a
signal resulting from a change in resistance of the detection
coil.
10. The proximity sensor according to claim 6, wherein the signal
in the second period is a signal resulting from the detection body,
and the controller performs the compensation by subtracting the
signal resulting from the change in the inductance of the detection
coil and the signal resulting from the change in the resistance of
the detection coil from the signal resulting from the detection
body.
11. The proximity sensor according to claim 7, wherein the signal
in the second period is a signal resulting from the detection body,
and the controller performs the compensation by subtracting the
signal resulting from the change in the inductance of the detection
coil and the signal resulting from the change in the resistance of
the detection coil from the signal resulting from the detection
body.
12. The proximity sensor according to claim 8, wherein the signal
in the second period is a signal resulting from the detection body,
and the controller performs the compensation by subtracting the
signal resulting from the change in the inductance of the detection
coil and the signal resulting from the change in the resistance of
the detection coil from the signal resulting from the detection
body.
13. The proximity sensor according to claim 9, wherein the signal
in the second period is a signal resulting from the detection body,
and the controller performs the compensation by subtracting the
signal resulting from the change in the inductance of the detection
coil and the signal resulting from the change in the resistance of
the detection coil from the signal resulting from the detection
body.
14. The proximity sensor according to claim 1, wherein the first
factor is a signal resulting from a change in inductance of the
detection coil or a signal resulting from a change in resistance of
the detection coil.
15. A method that is executed in a proximity sensor that detects
presence or position of a detection body by utilizing a magnetic
field, the method comprising: periodically supplying an excitation
current in a pulse form to a detection coil for generating the
magnetic field; performing detection of voltages or currents
generated at both ends of the detection coil by periodic supplying
the excitation current; acquiring a first factor that influences
detection of the detection body in a first period of a time series
signal obtained by the detection of the voltages or the currents
generated at both ends of the detection coil; performing
compensation on a signal in a second period of the time series
signal by the first factor; and detecting the presence or the
position of the detection body on the basis of a signal after the
compensation.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefit of Japan
application serial no. 2017-049731, filed on Mar. 15, 2017. The
entirety of the above-mentioned patent application is hereby
incorporated by reference herein and made a part of this
specification.
BACKGROUND
Technical Field
[0002] The disclosure relates to a proximity sensor and a detecting
method that is performed in a proximity sensor, and particularly to
an inductive proximity sensor and a detecting method that is
performed in an inductive proximity sensor.
Description of Related Art
[0003] A proximity sensor (inductive proximity sensor) that detects
the presence or position of a detection body made of a metal by
utilizing a magnetic field is known.
[0004] Patent Document 1 discloses a proximity sensor including a
detection coil that generates a magnetic field, an excitation
circuit that periodically supplies an excitation current in a pulse
form to the detection coil, a detection circuit that detects the
presence or position of a detection body made of a metal on the
basis of voltages generated at both ends of the detection coil
after the supply of the excitation current to the detection coil is
blocked, and a control circuit. The control circuit controls the
excitation circuit such that an excitation current supply period is
equal to or greater than an excitation current supply block
period.
[0005] In this manner, it is possible to suppress variation in a
detection distance due to a thickness of the detection body in a
case in which a material of the detection body is a non-magnetic
metal, representative examples of which include aluminum. Also, it
is possible to suppress variation in the detection distance of the
proximity sensor if the thickness is the same both in a case in
which the material of the detection body is iron and in a case in
which the material of the detection body is aluminum (see
"Abstract").
[0006] The proximity sensor described in Patent Document 1 can
reduce the variation in the detection distance due to the thickness
and the material of the detection body. According to such a
proximity sensor, there are cases in which detection coil
properties (an inductance component and a resistance component)
change due to an external magnetic field, a temperature, and the
like or the detection distance varies due to occurrence of
electromagnetic noise and the like.
PATENT DOCUMENTS
[0007] [Patent Document 1] Japanese Patent Application Laid-Open
(JP-A) No. 2009-59528
[0008] [Patent Document 2] Japanese Patent Application Laid-Open
(JP-A) No. 8-86773
SUMMARY
[0009] According to an aspect of the invention, a proximity sensor
detects the presence or position of a detection body by utilizing a
magnetic field. The proximity sensor includes: a detection coil
that generates a magnetic field; a transmission circuit that
periodically supplies an excitation current in a pulse form to the
detection coil; a reception circuit that detects voltages or
currents generated at both ends of the detection coil by the
periodic supply of the excitation current; and a controller that
detects the presence or the position of the detection body by
utilizing a time series signal obtained by the detection. The
controller acquires a first factor that influences the detection of
the detection body in a first period of the time series signal. The
controller compensates a signal in a second period of the time
series signal by the first factor. The controller detects the
presence or the position of the detection body on the basis of a
signal after the compensation.
[0010] According to another aspect of the invention, a detecting
method is executed in a proximity sensor that detects the presence
or position of a detection body by utilizing a magnetic field. The
detecting method includes periodically supplying an excitation
current in a pulse form to a detection coil for generating the
magnetic field; detecting voltages or currents generated at both
ends of the detection coil by the periodic supply of the excitation
current; acquiring a first factor that influences the detection of
the detection body in a first period of a time series signal
obtained by the detection; compensating a signal in a second period
of the time series signal by the first factor; and detecting the
presence or the position of the detection body on the basis of a
signal after the compensation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a diagram for explaining an outline of processing
that is executed by a controller of such a proximity sensor.
[0012] FIG. 2 is a diagram for explaining an outline of other
processing that is executed by the controller of the proximity
sensor.
[0013] FIG. 3 is a perspective view of the proximity sensor
according to the embodiment.
[0014] FIG. 4 is a sectional view taken along the arrow of the line
iv-iv in FIG. 3.
[0015] FIG. 5 is a block diagram for explaining a schematic
configuration of the proximity sensor.
[0016] FIG. 6 is a time chart of a signal that is generated or
received by the proximity sensor.
[0017] FIG. 7 is an enlarged view of main parts of a voltage signal
representing a detection coil voltage illustrated in FIG. 6 from a
time T0 to a time T1.
[0018] FIG. 8 is an enlarged view of main parts of the voltage
signal representing the detection coil voltage illustrated in FIG.
6 from the time T1 to a time T2.
[0019] FIG. 9 is a diagram for explaining the meanings of a
plurality of periods included in one cycle of the voltage signal
representing the detection coil voltage.
[0020] FIG. 10 is a diagram showing signal acquisition timing in an
excitation period and a block period.
[0021] FIG. 11 is a flowchart showing a flow of processing that is
executed by the proximity sensor.
[0022] FIG. 12 is a diagram showing a temporal change in the
detection coil voltage in a period Tx in a case in which there is
no detection body.
[0023] FIG. 13 is a diagram showing a temporal change in the
detection coil voltage in the period Tx in a case in which there is
a detection body.
[0024] FIG. 14 is a diagram showing a change rate obtained by
normalizing a detection body detection signal on the assumption
that there is no change in coil inductance in a case in which there
is a detection body.
[0025] FIG. 15 is a diagram showing a temporal change in the
detection coil voltage at and after a time Ta in a case in which
there is no detection body.
[0026] FIG. 16 is a diagram showing a temporal change in the
detection coil voltage at and after the time Ta in a case in which
there is a detection body.
[0027] FIG. 17 is a diagram showing a change rate obtained by
normalizing the detection body detection signal on the assumption
that there is no change in coil resistance in a case in which there
is a detection body.
[0028] FIG. 18 is a diagram for explaining processing when a change
in inductance of the detection coil is compensated for.
[0029] FIG. 19 is a diagram for explaining processing when a change
in resistance of the detection coil is compensated for.
[0030] FIG. 20 is a diagram for explaining processing when a change
in inductance of the detection coil and a change in resistance are
compensated for.
[0031] FIG. 21 is a diagram showing a noise removing circuit for
removing high-frequency noise.
DESCRIPTION OF THE EMBODIMENTS
[0032] One or some exemplary embodiments of the invention are made
in view of the above circumstances, and an inductive proximity
sensor and a method executed in an inductive proximity sensor
capable of reducing the influence of a change in coil properties
and/or the influence of disturbance noise are provided.
[0033] According to one or some exemplary embodiments of the
invention, the controller acquires a second factor that influences
the detection of the detection body in a third period of the time
series signal. The controller compensates the signal in the second
period of the time series signal by the first factor and the second
factor.
[0034] According to one or some exemplary embodiments of the
invention, the first period and the third period are included in a
period during which the excitation current is supplied. The second
period is included in a period during which the supply of the
excitation current is blocked.
[0035] According to one or some exemplary embodiments of the
invention, the first period, the second period, and the third
period are included in a period during which the excitation current
is supplied.
[0036] According to one or some exemplary embodiments of the
invention, the first period, the second period, and the third
period are included in a period in which the supply of the
excitation current is blocked.
[0037] According to one or some exemplary embodiments of the
invention, any one of the first factor and the second factor is a
signal resulting from a change in inductance of the detection coil,
and the other is a signal resulting from a change in resistance of
the detection coil.
[0038] According to one or some exemplary embodiments of the
invention, the signal in the second period is a signal resulting
from the detection body. The controller performs the compensation
by subtracting the signal resulting from the change in inductance
of the detection coil and the signal resulting from the change in
the resistance of the detection coil from the signal resulting from
the detection body.
[0039] According to one or some exemplary embodiments of the
invention, the first factor is a signal resulting from a change in
inductance of the detection coil or a signal resulting from a
change in resistance of the detection coil.
[0040] According to one or some exemplary embodiments of the
invention, it is possible to reduce the influence of a change in
coil properties and/or the influence of disturbance noise.
[0041] Hereinafter, embodiments of the invention will be described
with reference to the drawings. In the following description, the
same reference numerals will be given to the same components. The
names and the functions thereof are also the same. Therefore,
detailed description thereof will not be repeated.
A. OUTLINE OF PROCESSING
[0042] A proximity sensor according to the embodiment is an
inductive proximity sensor that detects the presence or position of
a detection body made of a metal by utilizing a magnetic field.
Although details will be described later, the proximity sensor
according to the embodiment compensates a signal for detection
using a signal in a section that has not been used for detecting
the detection body in the related art.
[0043] The proximity sensor includes at least a detection coil, a
transmission circuit, a reception circuit, and a controller. The
transmission circuit periodically supplies an excitation current in
a pulse form to the detection coil. Specifically, the transmission
circuit repeats supply and block of the excitation current. In this
manner, the detection coil generates a magnetic field. The
reception circuit detects voltages or currents generated at both
ends of the coil by the periodic supply of the excitation current.
The controller detects the presence or the position of the
detection body by utilizing a time series signal obtained by the
detection.
a1. First Processing Example
[0044] FIG. 1 is a diagram for explaining an outline of processing
that is executed by the controller of such a proximity sensor.
Referring to FIG. 1, the controller acquires a digitalized periodic
time series signal by the detection processing of the reception
circuit. A cycle .DELTA.T includes an excitation period during
which the excitation current is supplied and a block period during
which the supply of the excitation current is blocked.
[0045] The excitation period includes a time series signal D2 that
can be used for the detection of the detection body. The excitation
period includes a time series signal D1 as a signal in a previous
stage of the time series signal D2. Further, the excitation period
includes a time series signal D3 as a signal in a later stage of
the time series signal D2.
[0046] The block period also includes a time series signal D5 that
can be used for the detection of the detection body. The block
period includes a time series signal D4 as a signal in a previous
stage of the time series signal D5. Further, the block period
includes a time series signal D6 as a signal in a later stage of
the time series signal D5.
[0047] The controller acquires a factor that influences the
detection of the detection body from the time series signal D1
and/or the time series signal D3 in the excitation period. In a
typical example, the controller acquires a signal VLe resulting
from a change in inductance of the detection coil from the time
series signal D1. The controller acquires a signal VRe resulting
from a change in resistance of the detection coil from the time
series signal D3.
[0048] The controller acquires a signal VLs resulting from the
detection body from the time series signal D5 in the block period.
The signal VLs resulting from the detection body may be the time
series signal D5 itself or a part of the time series signal D5.
Further, the signal VLs resulting from the detection body may be
obtained by performing data processing, such as integration
processing, on the time series signal D5.
[0049] The controller compensates the signal VLs resulting from the
detection body using the acquired factor. Typically, the controller
compensates the signal VLs resulting from the detection body by
using at least one of the signal VLe resulting from the change in
the inductance and the signal VRe resulting from the change in the
resistance of the detection coil.
[0050] Specifically, the compensation of the signal VLs resulting
from the detection body is performed by subtracting the signal VLe
resulting from the change in the inductance and/or the signal VRe
resulting from the change in the resistance of the detection coil
from the signal VLs resulting from the detection body.
[0051] The controller detects the presence or the position of the
detection body by using the signal VLs after the compensation.
Therefore, the proximity sensor with such a configuration can
reduce the influence of changes in coil properties (an inductance
component, a resistance component).
a2. Second Processing Example
[0052] FIG. 2 is a diagram for explaining an outline of other
processing that is executed by the controller of the proximity
sensor. Referring to FIG. 2, the controller 60 acquires a factor
that influences the detection of the detection body from the time
series signal D1 and/or the time series signal D3 in the excitation
period. Typically, the controller 60 acquires the signal VLe
resulting from a change in the inductance of the detection coil
from the time series signal D1. The controller acquires the signal
VRe resulting from a change in the resistance of the detection coil
from the time series signal D3.
[0053] The controller 60 acquires the signal VLs resulting from the
detection body from the time series signal D2 in the excitation
period. In this manner, this configuration is different from the
configuration in which the signal VLs is acquired from the time
series signal D5 in the block period as illustrated in FIG. 1 in
that the signal VLs is acquired from the time series signal D2 in
the excitation period.
[0054] The controller 60 compensates the signal VLs acquired in the
excitation period by using the factor acquired in the excitation
period. Typically, the controller 60 compensates the signal
[0055] VLs resulting from the detection body by using at least one
of the signal VLe resulting from the change in the inductance and
the signal VRe resulting from the change in the resistance of the
detection coil in the same manner as in the case illustrated in
FIG. 1.
[0056] The proximity sensor with such a configuration can also
reduce the influence of changes in the coil properties (the
inductance component and the resistance component).
[0057] Although the processing illustrated in FIG. 2 has a
configuration that focuses on the excitation period, the signal VLs
resulting from the detection body may be compensated using the time
series signals D4 to D6 in the block period. That is, the
controller 60 may compensate the signal VLs acquired in the block
period using the aforementioned factor acquired in the block period
and detect the presence or the position of the detection body using
the signal VLs after the compensation.
[0058] Hereinafter, a structure of the proximity sensor will be
described with reference to drawings, and details of processing
that is executed by the proximity sensor will be described
appropriately referring to the drawings.
[0059] Hereinafter, the signal VLs resulting from the detection
body will also be referred to as a "detection body detection signal
VLs," the signal VLe resulting from a change in the inductance will
be referred to as a "coil inductance detection signal VLe," and the
signal VRe resulting from a change in the resistance of the
detection coil 11 will be referred to as a "coil resistance
detection signal VRe" for convenience of description.
B. SENSOR STRUCTURE
[0060] FIG. 3 is a perspective view of the proximity sensor 1
according to the embodiment. Referring to FIG. 3, the proximity
sensor 1 includes a main body 5, a lead line 6 that is connected to
the main body 5, nuts 7 and 8, and a washer 9 that is arranged
between the nuts 7 and 8.
[0061] The main body 5 has a circular detection surface 5a and a
tubular case body 5b. Thread grooves for the nuts 7 and 8 are
formed in the surface of the case body 5b. The detection surface 5a
is part of a cap that is fit to the case body 5b.
[0062] The nuts 7 and 8 and the washer 9 are used for attaching the
proximity sensor 1 to a support member of a device or the like. For
example, the main body 5 can be fixed to the support member by
pinching a part of an attachment tool (an L-shaped tool, for
example) between the nuts 7 and 8.
[0063] FIG. 4 is a sectional view taken along the arrow of the line
iv-iv in FIG. 3. Referring to FIG. 4, the main body 5 has a
detection coil 11, a ferrite core 15, an electronic circuit 17
(hybrid IC) with elements arranged on a substrate, and an operation
display light which is not illustrated in the drawing. The main
body 5 is filled with resin.
[0064] The detection coil 11 is an annular coil. The center of the
detection coil 11 is positioned on a central axis M of the main
body 5. The detection coil 11 is electrically connected to the
electronic circuit 17. The electronic circuit 17 is supplied with
electricity via the lead line 6 and is electrically connected to an
external electronic device.
[0065] If a high-frequency magnetic field is generated by causing
an excitation current to flow through the detection coil 11, an
eddy current (inductive current) flows through a detection body
700. Inductive voltages (transient signals) are generated at both
ends of the detection coil 11 by the eddy current. The proximity
sensor 1 detects these inductive voltages. In this manner, the
proximity sensor 1 detects the presence of the detection body 700.
The proximity sensor 1 is not limited thereto and may have another
configuration for detecting the position of the detection body
700.
[0066] FIG. 5 is a block diagram for explaining a schematic
configuration of the proximity sensor 1. Referring to FIG. 5, the
proximity sensor 1 includes a detector 30, a transmission circuit
40, a reception circuit 50, a controller 60, and an output part 70.
The transmission circuit 40, the reception circuit 50, the
controller 60, and the output part 70 are realized as the
electronic circuit 17.
[0067] The detector 30 includes a coil 11 and a discharge
resistance 12. The controller 60 has a control circuit 61 and a
computation circuit 62. The output part 70 includes an output
circuit 71. The transmission circuit 40 includes an excitation
circuit 41. The reception circuit 50 includes a filter circuit 51,
an amplification circuit 52, and an analog/digital (A/D) conversion
circuit 53.
[0068] The controller 60 controls overall operations of the
proximity sensor 1. The control circuit 61 of the controller 60
transmits an excitation control signal for controlling a timing of
excitation to the transmission circuit 40.
[0069] The excitation circuit 41 that serves as the transmission
circuit 40 generates an excitation current in a pulse form on the
basis of the excitation control signal and outputs the excitation
current to the detector 30.
[0070] The reception circuit 50 detects a voltage or a current
generated by the detector 30 by the supply and the block of the
excitation current. Specifically, the reception circuit 50 detects
voltages (voltage signals) generated at both ends of the detection
coil 11. The reception circuit 50 outputs the detection result to
the controller 60. The reception circuit 50 will be described in
detail below.
[0071] An analog signal that represents the detection result of the
detection coil 11 is input to the filter circuit 51. The filter
circuit 51 performs predetermined filtering processing on the input
analog signal in order to remove noise.
[0072] The amplification circuit 52 amplifies the analog signal, on
which the filtering processing has been performed, and outputs an
analog signal after the amplification to the A/D conversion circuit
53.
[0073] The A/D conversion circuit 53 converts the analog signal
that has been amplified by the amplification circuit 52 into a
digital signal. The A/D conversion circuit 53 outputs the digital
signal to the computation circuit 62.
[0074] The computation circuit 62 of the controller 60 performs
computation, which will be described later, on a signal output from
the reception circuit 50 and outputs a computation result (signal)
to the output part 70.
[0075] The output part 70 transmits the signal (detection result)
sent from the controller 60 to an electronic device as a connection
source of the proximity sensor 1 via the lead line 6.
[0076] As described above, the proximity sensor 1 detects the
presence or the position of the detection body 700 by utilizing a
magnetic field. The proximity sensor 1 has a configuration
including (i) the detection coil 11 that generates a magnetic
field, (ii) the transmission circuit 40 that periodically supplies
an excitation current in a pulse form to the detection coil 11,
(iii) the reception circuit 50 that detects voltages or currents
generated at both ends of the detection coil 11 by the periodic
supply of the excitation current, and (iv) the controller 60 that
detects the presence or the position of the detection body 700 by
utilizing a time series signal obtained by the detection.
[0077] The proximity sensor 1 may include a plurality of coils in
the detector 30. For example, a case in which the detection coil 11
includes a transmission coil and a reception coil is exemplified.
Although the controller normally executes filtering processing
based on a filtering coefficient acquired in the excitation period,
the reception circuit 50 may perform the filtering processing
executed by the controller 60 by passing the filtering coefficient
from the computation circuit 62 to the reception circuit 50 and
changing the filtering coefficient of the reception circuit 50.
C. DATA PROCESSING
[0078] Hereinafter, a case in which the first processing is mainly
performed from among the aforementioned first processing example
(FIG. 1) and the second processing example (FIG. 2) will be
exemplified and described.
[0079] (C1. Time Chart)
[0080] FIG. 6 is a time chart of a signal that is generated or
received by the proximity sensor 1. Referring to FIG. 6, if an
excitation control signal to be sent from the control circuit 61 to
the excitation circuit 41 rises at a time T0 as illustrated in a
graph (i), the excitation circuit 41 supplies a current. Then, a
current rises with a predetermined time constant in the detection
coil 11 as illustrated in a graph (ii), and an inductive voltage
generated at the time of the start of the excitation settles down
with a predetermined time constant as illustrated in a graph
(iii).
[0081] If the excitation current is blocked at a time T1 that comes
.DELTA.Te hours later than the time T0 as illustrated in the graph
(i), the current falls with a predetermined time constant as
illustrated in the graph (ii), and the inductive voltage that is
generated in the direction opposite to that when the excitation is
started settles down with a predetermined time constant as
illustrated in the graph (iii).
[0082] The phenomenon from the time T0 to a time T2 is repeated
even at and after the time T2 that comes a cycle .DELTA.T later
than the time T0.
[0083] (C2. Method of Deciding Coil Signal Acquisition Time)
[0084] FIG. 7 is an enlarged view of main parts of the voltage
signal (graph (iii)) representing the detection coil voltage
illustrated in FIG. 6 from the time T0 to the time T1. FIG. 8 is an
enlarged view of main parts of the voltage signal representing the
detection coil voltage illustrated in FIG. 6 from the time T1 to
the time T2. FIG. 9 is a diagram for explaining the meanings of a
plurality of periods included in one cycle of the voltage signal
representing the detection coil voltage.
[0085] The inductive voltage generated in the detection coil 11
immediately after the start of the supply of the excitation current
or immediately after the block of the excitation steeply decreases
due to the discharge resistance 12 that is connected to the
detection coil 11 in parallel. In a case in which the detection
body 700 has approached the proximity sensor 1, the inductive
voltage is further generated in the detection coil 11 due to the
influence of an eddy current generated in the detection body 700
when the excitation of the excitation current is started or the
excitation current is blocked.
[0086] A resistance value of the discharge resistance 12 is set
such that the time constant of the inductive voltage generated by
the detection body 700 becomes greater than the time constant of
the circuit that includes the detection coil 11 and the discharge
resistance 12. Therefore, the inductive voltage of the detection
coil 11 itself is dominant as the detection coil voltage until a
specific time after the start of the excitation of the excitation
current or after the block of the excitation current, and the
inductive voltage due to the eddy current is dominant at and after
the time.
[0087] Referring to FIGS. 7 and 8, the graph represented by the
dotted line represents the detection coil voltage. The graph
represented by the broken line represents the inductive voltage of
the detection coil itself. The graph represented by the solid line
represents the inductive voltage of the detection body. The
detection coil voltage is represented as a sum of the inductive
voltage of the detection coil itself and the inductive voltage of
the detection body. The hatched regions in the drawings are
integration data of the inductive voltage of the detection body
700.
[0088] Referring to FIG. 9, the inductive voltage of the detection
coil 11 is dominant as the detection coil voltage in the period Tx
(from the time T0 to a time Ta) from the start of the excitation of
the excitation current to a specific time. In the following period
Ty (from the time Ta to a time Tb), the inductive voltage due to
the eddy current is dominant. The inductive voltage of the
detection coil 11 itself is dominant as the detection coil voltage
in a period Tx' (from the time T1 to a time Tc) from the block of
the excitation current to a specific time. In the following period
Ty' (from the time Tc to a time Td), the inductive voltage due to
the eddy current is dominant.
[0089] If the inductance of the detection coil changes due to a
direct magnetic field and the like, the time constant of the
detector changes. Therefore, the computation circuit 62 can acquire
the change in the inductance by using a change in the voltage in
the periods Tx and Tx' (from the time T0 to the time Ta and from
the time T1 to the time Tc) during which the inductive voltage of
the detection coil itself is dominant.
[0090] In a period Tz (from the time Tb to the time T1) during
which the inductive voltage of the detection coil 11 and the
detection body 700 settle down during the excitation, the voltage
generated in the detection coil 11 has a magnitude that depends on
a direct current resistance value of the detection coil 11 and the
excitation current. Therefore, the computation circuit 62 can
acquire a change in the resistance value of the detection coil 11
due to a variation in temperature or the like by using the voltage
in the period Tz (rom the time Tb to the time T1).
[0091] Therefore, the signal representing a change in the
inductance may be acquired by using a part of the detection coil
voltage in the period Tz (or the period Tx'). Meanwhile, the signal
representing a change in the resistance may be acquired by using a
part of the detection coil voltage in the period Tz.
[0092] (C3. Method of Acquiring Change in Coil Properties)
[0093] FIG. 10 is a diagram showing signal acquisition timing in
the excitation period and the block period. Referring to FIG. 10,
the computation circuit 62 acquires a detection coil voltage in a
period .DELTA.Tgp1. The period .DELTA.Tgp1 is selectively set by
the acquired factor. In the case of acquiring the coil inductance,
a time Tge after the excitation start time T0 may be set, and a
time Tgf before the time Ta may be set. In the case of acquiring
coil resistance, the time Tge after the time Tb may be set and the
time Tgf before the block period start time T1 (=T0+.DELTA.Te) may
be set. In the case of acquiring both the coil inductance and the
coil resistance, the time Tge after the excitation start time T0
may be set, and the time Tgf before the block period start time T1
may be set.
[0094] The computation circuit 62 acquires at least one of a
detection signal (specifically, a coil inductance detection signal
VLe) obtained by performing predetermined processing on the signal
in the period Tx (from the time T0 to the time Ta) illustrated in
FIG. 9 and a detection signal (specifically, a coil resistance
detection signal VRe) obtained by performing predetermined
processing on the signal in the period Tz (from the time Tb to the
time T1) illustrated in FIG. 9 from among the acquired detection
coil voltages.
[0095] The computation circuit 62 acquires a detection coil voltage
in a period .DELTA.Tgp2. The period .DELTA.Tgp2 is a period from a
time Tgs that comes after the block start time T1 (=T0+.DELTA.Te)
to a time Tgu that comes before the excitation period start time
T2. As the period .DELTA.Tgp2, a time during which the influence of
the detection body can be effectively acquired in the signal from
the time Tc to the time Td may be selected.
[0096] The computation circuit 62 acquires a detection body
detection signal VLs from among the acquired detection coil
voltages. Specifically, the computation circuit 62 acquires the
detection body detection signal VLs by using the detection coil
voltage in the period Ty' (from the time Tc to the time Td)
illustrated in FIG. 9.
[0097] The computation circuit 62 compensates the detection body
detection signal VLs using at least one of the coil inductance
detection signal VLe and the coil resistance detection signal VRe.
In this manner, the computation circuit 62 can acquire a detection
body determination signal that is not influenced by a change in
coil properties.
[0098] FIG. 11 is a flowchart showing a flow of processing that is
executed by the proximity sensor 1. Referring to FIG. 11, the
excitation circuit 51 starts pulse excitation on the basis of an
excitation control signal from the control circuit 61 in Step S1.
In Step S2, the computation circuit 62 acquires a signal (detection
coil voltage) in the period .DELTA.Tgp1 (see FIG. 10).
[0099] In Step S3, the excitation circuit 41 blocks the pulse
excitation after elapse of a time .DELTA.Te from the pulse
excitation. In Step S4, the computation circuit 62 acquires a
signal (detection coil voltage) in a period .DELTA.Tgp2 (see FIG.
10).
[0100] In Step S5, the computation circuit 62 compensates the
detection body detection signal VLs using at least one of the coil
inductance detection signal VLe and the coil resistance detection
signal VRe. The computation circuit 62 temporarily stores the
signal VLs after the compensation.
[0101] In Step S6, it is determined whether or not the number of
times of the pulse excitation has reached N or greater (N is a
natural number set in advance). In a case in which it is determined
that the number of times is less than N (No in Step S6), the
processing is returned to Step S1. In a case in which it is
determined that the number of times is equal to or greater than N
(Yes in Step S6), N signals VLs after the compensation are averaged
in Step S7.
[0102] In Step S8, the computation circuit 62 compares the averaged
signal VLs after the compensation with a preset threshold value. In
Step S9, the computation circuit 62 determines the presence of the
detection body 700 on the basis of the comparison result and causes
the output part 70 to output the result.
[0103] In the case of a configuration in which the computation
circuit 62 determines the position of the detection body 700 rather
than the determination of the presence of the detection body 700,
the computation circuit 62 converts the averaged signal VLs after
the compensation into positional information instead of the
processing in Step S8. Further, the computation circuit 62 causes
the output part 70 to output the positional information of the
detection body 700 instead of the processing in Step S9.
[0104] (1) Influence of Change in Inductance
[0105] In a case in which a change in the inductance of the
detection coil 11 has occurred, the change in the inductance
appears in the magnitude of the voltage in the period Tx (from the
time T0 to the time Ta) during which the inductive voltage of the
detection coil 11 itself is dominant in the period .DELTA.Tgp1 (see
FIG. 10). In the period .DELTA.Tgp2, the inductive voltage of the
detection coil 11 itself becomes small, and the influence of the
eddy current due to the detection body 700 appears dominantly.
Although the influence of the change in the inductance of the
detection coil 11 itself also appears in the voltage signal
representing the influence of the eddy current due to the detection
body 700 in the period .DELTA.Tgp2 at this time, this can be
compensated for by the signal acquired in the period
.DELTA.Tgp1.
[0106] FIG. 12 is a diagram showing a temporal change in the
detection coil voltage in the period Tx (from the time T0 to the
time Ta) in a case in which there is no detection body 700. FIG. 13
is a diagram showing a temporal change in the detection coil
voltage in the period Tx (from the time T0 to the time Ta) in a
case in which there is a detection body 700.
[0107] Referring to FIG. 12, the graph of the solid line represents
a reference detection coil voltage in the case in which there is no
detection body 700, and the graph of the broken line represents a
detection coil voltage when there is a change in the inductance in
the case in which there is no detection body 700. Referring to FIG.
13, the graph of the solid line represents a reference detection
coil voltage in the case in which there is a detection body 700,
and the graph of the broken line represents a detection coil
voltage when there is a change in the inductance in the case in
which there is a detection body 700.
[0108] There is a correlation between the coil inductance detection
signal VLe generated by the signal in the period Tx (from the time
T0 to the time Ta) during which the inductive voltage of the
detection coil 11 itself is dominant in the period .DELTA.Tgp1 and
the detection body detection signal VLs generated by the detection
coil voltage in the period .DELTA.Tgp2. Therefore, the computation
circuit 62 calculates the amount of change due to the inductance on
the basis of the amount of change in the coil inductance detection
signal VLe from the reference (that is, in the case in which there
is no change in the inductance) coil inductance detection signal
VLe, and subtracts the calculated amount of change from the
detection body detection signal VLs. In this manner, an effect of
compensating for the influence of the change in the inductance can
be obtained.
[0109] FIG. 14 is a diagram showing a change rate obtained by
normalizing the detection body detection signal Vls on the
assumption that there is no change in the coil inductance in the
case in which there is a detection body 700. Referring to FIG. 14,
in the case in which there is a change in the inductance, the
change rate approaches 1 when the above compensation is performed
as compared with a case in which no compensation is performed. That
is, it is possible to obtain a result that is closer to that in the
case in which there is no change in the inductance by the above
compensation. That is, it is possible to obtain the effect of
compensating for the influence of the change in the inductance as
described above.
[0110] (2) Influence of Change in Resistance
[0111] In a case in which a change in the resistance of the
detection coil 11 has occurred, the change in the coil resistance
appears in the magnitude of the voltage in a period (from the time
Tb to the time T1) during which the inductive voltage is not
generated in the period .DELTA.Tgp1 (see FIG. 10). Although the
influence of the change in the resistance of the detection coil 11
also appears in the voltage signal representing the influence of
the eddy current due to the detection body 700 in the period
.DELTA.Tgp2, this can be compensated for by the signal acquired in
the period .DELTA.Tgp1.
[0112] FIG. 15 is a diagram showing a temporal change in the
detection coil voltage at and after the time Ta (including the time
Tb) in the case in which there is no detection body 700. FIG. 16 is
a diagram showing a temporal change in the detection coil voltage
at and after the time Ta (including the time Tb) in the case in
which there is a detection body 700.
[0113] Referring to FIG. 15, the graph of the solid line represents
a reference detection coil voltage in the case in which there is no
detection body 700, and the graph of the broken line represents a
detection coil voltage when there is a change in the coil
resistance in the case in which there is no detection body 700.
Referring to FIG. 16, the graph of the solid line represents a
reference detection coil voltage in the case in which there is a
detection body 700, and the graph of the broken line represents a
detection coil voltage when there is a change in the coil
resistance in the case in which there is a detection body 700.
[0114] There is a correlation between the coil resistance detection
signal VRe generated by the signal after the inductive voltage in
the period .DELTA.Tgp1 completely settles down (at and after the
time Tb) and the detection body detection signal VLs generated by
the voltage signal in the period .DELTA.Tgp2. Therefore, the
computation circuit 62 calculates the amount of change due to the
resistance on the basis of the amount of change in the coil
resistance detection signal VRe from the reference (that is, in the
case in which there is no change in the coil resistance) coil
resistance detection signal VRe, and subtracts the calculated
amount of change from the detection body detection signal VLs. In
this manner, an effect of compensating for the influence of the
change in the coil resistance can be obtained.
[0115] FIG. 17 is a diagram showing a change rate obtained by
normalizing the detection body detection signal VLs on the
assumption that there is no change in the coil resistance in a case
in which there is a detection body 700. Referring to FIG. 17, the
change rate approaches 1 as compared with a case in which no
compensation is performed, by performing the above compensation in
the case in which there is a change in the coil resistance. That
is, it is possible to obtain a result similar to that in the case
in which there is no change in the coil resistance by performing
the above compensation. That is, the effect of compensating the
influences of the change in the coil resistance is obtained as
described above.
[0116] (C4. Compensation Method)
(1) Compensation of Change in Inductance
[0117] FIG. 18 is a diagram for explaining processing when the
change in the inductance of the detection coil 11 is compensated
for. That is, FIG. 18 is a diagram for explaining processing when
the detection body detection signal VLs is compensated using the
coil inductance detection signal VLe.
[0118] Referring to FIG. 18, a correlation equation between the
change rate of the coil inductance detection signal VLe and the
change rate of the detection body detection signal VLs for the
detection coil voltage (voltage signal) in a reference state in
which no change has occurred in the inductance of the detection
coil 11 is calculated in a design stage or a fabrication stage of
the proximity sensor 1.
[0119] The computation circuit 62 of the proximity sensor 1
calculates a compensation coefficient on the basis of the change
rate of the coil inductance detection signal VLe from the reference
signal and the aforementioned correlation equation calculated in
advance at the time of the detection. The computation circuit 62
compensates the detection body detection signal VLs using the
compensation coefficient.
(2) Compensation of Change in Coil Resistance
[0120] FIG. 19 is a diagram for explaining processing when a change
in the resistance of the detection coil 11 is compensated for. That
is, FIG. 19 is a diagram for explaining processing when the
detection body detection signal VLs is compensated using the coil
resistance detection signal VRe.
[0121] Referring to FIG. 19, a correlation equation between the
change rate of the coil resistance detection signal VRe and the
change rate of the detection body detection signal VLs for the
detection coil voltage (voltage signal) in the reference state in
which no change has occurred in the resistance of the detection
coil 11 in the design stage or the fabrication stage of the
proximity sensor 1.
[0122] The computation circuit 62 of the proximity sensor 1
calculates a compensation coefficient on the basis of the change
rate of the coil resistance detection signal VRe from the reference
signal and the aforementioned correlation equation calculated in
advance at the time of the detection. The computation circuit 62
compensates the detection body detection signal VLs using the
compensation coefficient.
(3) Compensation of Change in Inductance and Change in Coil
Resistance
[0123] FIG. 20 is a diagram for explaining processing when a change
in the inductance and a change in the resistance of the detection
coil 11 are compensated for. That is, FIG. 20 is a diagram for
explaining processing when the detection body detection signal VLs
is compensated using the coil inductance detection signal VLe and
the coil resistance detection signal VRe.
[0124] Referring to FIG. 20, The correlation equation between the
change rate of the coil inductance detection signal VLe and the
coil resistance detection signal VRe and the change rate of the
detection body detection signal VLs is calculated for the detection
coil voltage (voltage signal) in the reference state in which no
change has occurred in the inductance and the resistance of the
detection coil 11, in the design stage or the fabrication stage of
the proximity sensor 1.
[0125] The computation circuit 62 of the proximity sensor 1
calculates a compensation coefficient on the basis of the change
rate of the coil inductance detection signal VLe from the reference
signal, the change rate of the coil resistance detection signal VRe
from the reference signal, and the aforementioned correlation
equation calculated in advance at the time of the detection. The
computation circuit 62 compensates the detection body detection
signal VLs using the compensation coefficient.
D. REMOVAL OF HIGH-FREQUENCY NOISE
[0126] As one form of the compensation of the detection body
detection signal VLs, a method of removing high-frequency noise due
to a disturbance will be described.
[0127] The proximity sensor 1 has a possibility of various kinds of
noise such as inverter noise, radiated emission noise, and power
source line noise being constantly added to the detection coil
voltage (voltage signal). Thus, the noise components are obtained
in the period Tx, Tx' (see FIG. 9) during which the inductive
voltage of the detection coil 11 itself is dominant or the period
Tz, Tz' during which the resistance value of the detector 30 is
dominant. Further, the calculated noise components are subtracted
from the detection coil voltage in the period Ty, Ty' during which
the inductive voltage of the detection body 700 is dominant.
Hereinafter, a specific example of the processing will be
described.
[0128] FIG. 21 is a diagram showing a noise removing circuit 210
for removing high-frequency noise. Referring to FIG. 21, the noise
removing circuit 210 includes a fast Fourier transform (FFT) part
211, a filter coefficient calculator 212, and a filter 213.
Although the noise removing circuit 210 is typically executed by
the computation circuit 62 of the controller 60, the filtering
processing executed by the controller 60 may instead be performed
by the reception circuit 50 by passing the filter coefficient from
the computation circuit 62 to the reception circuit 50 and changing
the filter coefficient of the reception circuit 50.
[0129] Since the detection coil voltage (voltage signal) is
constant in a period during which no inductive voltage is generated
by the start of the excitation or the block (for example, at or
after the time Tb), it is possible to stably observer the
superimposed high-frequency noise. Thus, the FFT part 211
calculates the frequency of the superimposed noise by performing
frequency analysis on a time series signal at and after the time Tb
in the period .DELTA.Tgp1 (see FIG. 10).
[0130] The filter coefficient calculator 212 obtains a filter
coefficient corresponding to the calculated noise frequency. The
filter 213 applies a filter for which the calculated filter
coefficient is set on the time series signal acquired from the
detector 30. In this manner, it is possible to remove noise with a
high effect in a previous stage of the filter circuit 51.
[0131] If the computation circuit 62 specifies the noise component,
it becomes unnecessary for the filter 213 to perform the filtering
processing, by changing the filter coefficient of the filter
circuit 51. Therefore, the filter 213 is activated or deactivated
in response to a control command.
E. EFFECTS
[0132] Effects Obtained by the Proximity Sensor 1 Will be Listed
Below.
[0133] (1) The inductance component and/or the resistance component
of the detection coil 11 at the time of the measurement is acquired
by observing how the voltage changes in the pulse excitation
period, and in accordance with this, the detection body detection
signal VLs is compensated. Therefore, it is possible to reduce the
influence of the change in the inductance due to a direct current
magnetic field or the like and/or the influence due to a change in
the temperature. Further, it is possible to effectively remove the
noise by measuring the frequency of the superimposed noise in the
pulse excitation period and setting the filter coefficient.
[0134] (2) Even when a change in the coil inductance due to the
direct current magnetic field, the low-frequency magnetic field, or
the like, a change in the coil resistance due to a change in the
temperature, or superimposition of electromagnetic noise or the
like on the detection signal occurs, it is possible to prevent the
determination result of the proximity sensor 1 from being
influenced by the occurrence. This phenomenon enables the user to
stably perform detection in an environment in which a variation in
the temperature occurs or in a magnetic field environment.
[0135] (3) The magnitude of the external magnetic field, the
temperature, and the frequency of the high-frequency noise can be
sensed (output). The aforementioned compensation can also be
applied to compensation of individual variations in the inductance
component and the resistance component of the detection coil in the
fabrication stage of the proximity sensor 1.
F. CONCLUSION
[0136] (1) The proximity sensor 1 detects the presence or the
position of the detection body by utilizing a magnetic field. The
proximity sensor 1 includes the detection coil 11 that generates
the magnetic field, the transmission circuit 40 that periodically
supplies an excitation current in the pulse form to the detection
coil 11, the reception circuit 50 that detects voltages or the
currents generated at both ends of the detection coil 11 by the
periodic supply of the excitation current, and the controller 60
that detects the presence or the position of the detection body 700
by utilizing the time series signal obtained by the detection.
[0137] The controller 60 acquires the first factor that influences
the detection of the detection body 700 in the first period of the
time series signal. The controller 60 compensates the signal in the
second period of the time series signal by the first factor. The
controller 60 detects the presence or the position of the detection
body 700 on the basis of the signal after the compensation.
[0138] With such a configuration, it is possible to reduce the
influence of a change in the coil properties of the detection coil
11 and/or the influence of disturbance noise.
[0139] (2) The controller 60 acquires the second factor that
influences the detection of the detection body in the third period
of the time series signal. The controller 60 compensates the signal
in the second period of the time series signal by the first factor
and the second factor.
[0140] (3) The first period and the second period are included in
the period during which the excitation current is supplied (the
excitation period .DELTA.Te in FIG. 6). The third period is
included in the period during which the supply of the excitation
current is blocked (block period).
[0141] In another aspect, the first period, the second period, and
the third period are included in the period during which the
excitation current is supplied (the excitation period .DELTA.Te) as
illustrated in FIG. 2. The first period, the second period, and the
third period are included in the period during which the supply of
the excitation current is blocked (block period).
[0142] (4) Any one of the first factor and the second factor is the
signal resulting from a change in the inductance of the detection
coil 11 (the coil inductance detection signal VLe), and the other
is the signal resulting from a change in the resistance of the
detection coil 11 (the coil resistance detection signal VRe).
[0143] (5) The signal in the second period is the signal resulting
from the detection body (the detection body detection signal VLs).
The controller 60 compensates the signal resulting from the
detection body (the detection body detection signal VLs) by
subtracting the signal resulting from the change in the inductance
of the detection coil 11 (the coil inductance detection signal VLe)
and the signal resulting from the change in the resistance of the
detection coil 11 (the coil resistance detection signal VRe) from
the signal resulting from the detection body (the detection body
detection signal VLs).
[0144] (6) The first factor is the signal resulting from the change
in the inductance of the detection coil (the coil inductance
detection signal VLe) or the signal resulting from the change in
the resistance of the detection coil (the coil resistance detection
signal VRe).
[0145] It will be apparent to those skilled in the art that various
modifications and variations can be made to the disclosed
embodiments without departing from the scope or spirit of the
disclosure. In view of the foregoing, it is intended that the
disclosure covers modifications and variations provided that they
fall within the scope of the following claims and their
equivalents.
* * * * *